Until noon, hundreds of Newark police officers in black rain slickers outnumbered spectators gathering on the streets near Sacred Heart Cathedral for a glimpse of the Pope.

Around the cathedral, officers from the Essex County Sheriff's office lifted manhole covers and peered inside with flashlights and looked into garbage cans. Whenever a window opened across the street from the cathedral, a half-dozen officers shouted to close it.

When more than a hundred flowerpots of bright yellow chrysanthemums were delivered to the front of the cathedral at 8:30 A.M. yesterday, Secret Service agents -- conspicuous in their dark suits, ties and gold lapel pins -- stuck probes into the pots to make sure they contained nothing but soil before they were set around the arched Gothic cathedral.

At the airport, Barry and Bobbie, two Belgian Malinois bomb-sniffing dogs, checked packages, briefcases and television gear, while 2,000 parochial-school students, priests and other dignitaries greeting the Pope funneled through metal detectors.

To guard the Pope as well as foreign dignitaries gathering for the 50th anniversary of the United Nations, the Secret Service has put together the largest force of Federal agents ever, according to Special Agent Gerry Byrnes, a spokesman for the service.

"The Secret Service is concerned with what's above, below and around the Pope during his visit to New York City," Mr. Byrnes said, adding that details were, naturally, secret.

While security officials, as is customary, refused to put any numbers on their deployment, unofficial estimates were that 3,000 Federal officials and 5,000 New York City police officers were to guard the Pope.

The block of East 72d Street between Fifth and Madison Avenues, where the Pope is staying at the residence of the Holy See's Permanent Mission to the United Nations, was sealed off by police barricades yesterday. Two white catering tents formed a kind of tunnel from the street to the ornate front door decorated with the Vatican seal of crossed keys.

Among the 18 New York City agencies coping with the Pope's visit is the Department of Transportation, 15 of whose employees were huddled last night in a 10th-floor communication center at 40 Worth Street filled with the babble of 12 radio channels, 3 television sets and 75 telephones ("for irate citizens," a worker said), constantly monitoring accidents, holes in the pavement or anything else that would disrupt traffic, including the Pope's motorcade of armored limousines and motorcycle escorts up the F.D.R. Drive to 72d Street.

"You name it, we're on top of it," said John Pimentel, the tour commander, interrupting himself to advise a caller: "Stay away from the East Side tonight."

At 7:50 P.M., the Pope's helicopter landed at the East River heliport near Wall Street. The F.D.R. Drive was closed for almost an hour to accommodate the motorcade, snarling traffic along the way. Around 5 P.M., on the way from the Newark airport to Sacred Heart Cathedral, the motorcade had also disrupted rush-hour traffic on the New Jersey Turnpike, which was backed up for six miles.

But experts said the Yom Kippur holiday meant there was less traffic than normal.